Grade 3 Skills Workbook (Unit 5)

Did you know that the sun is the greatest source of light for our planet, Earth? But what is light? Why is it so important?

Hot gases from the sun give off both light and heat energy. Light carries energy. Long wavelengths (the length of one light wave) carry the least energy, and short wavelengths carry the most. When you think of something with lots of energy, what comes to mind?

Do you think of something fast, like a race car? Do you think of something with great force, like a strong wind knocking down a tree?

Believe it or not, light can be many times more energetic than a car or the wind.

Light travels at 186,000 miles every second in a vacuum (empty space with no air). At that speed, light could go around Earth more than seven times every second! No human-made machine can go that fast—not even a jet plane or a rocket!

One way that light travels, including light from the sun, is in the form of waves. Scientists can measure how long light waves are. Waves can be different sizes—some are long and some are short. Some light waves are visible (able to be seen) and some are invisible. Whether you can see a light wave or not depends on how long the wave is. The longest wavelength of visible light looks red, and the shortest wavelength looks violet. Short wavelengths carry the most energy.

The sun gives off what is called white light. You might think the light from the sun has no color at all. Or maybe you think the sun's light looks more yellow. It may surprise you to learn that the sun's white light is actually made up of all the colors of the rainbow. White light includes light of many different wavelengths, including every color we can see.

Of all the wavelengths in the sun's light, there is just a little more yellow than the other colors. This is why the sun looks yellow when we see it against the blue sky. Still, the sun's light includes all the other colors and wavelengths too. You will learn more about white light, visible light, and colors in a later chapter of this Reader.